The invention relates generally to marine propulsion device such as outboard motors including two-stroke internal combustion engines. The invention also relates to so called "tuning" of such engines, i.e., to timing of the arrival of returning acoustical pressure waves at the cylinder exhaust ports. In addition, the invention relates to catalytic treatment of the exhaust gases of such engines to reduce emission of pollutants.
Attention is directed to the following U.S. Pat. Nos:
______________________________________ 3,939,807 Eichinger February 24, 1976 4,312,422 Matsushita, et al. January 26, 1982 4,337,054 Holtermann, et al. June 29, 1982 4,660,738 Scharpf April 28, 1987 4,735,046 Iwai April 5, 1988 4,772,236 Takahashi September 20, 1988 4,800,720 Okada January 31, 1989 4,848,082 Takahashi, et al. July 18, 1989 4,900,282 Takahashi, et al. February 13, 1990 4,940,435 Osborn, et al. July 10, 1990 4,966,567 Breckenfeld, et al. October 30, 1990 5,100,351 Shibata March 31, 1992 5,174,112 Sougawa, et al. December 29, 1992 5,212,949 Shiozawa May 25, 1993 FOREIGN PATENTS Japanese Patent Public February 16, 1988 Disclosure No. 36014/88 German Patent DE 3736500 A1 November 5, 1989 Japanese Patent Public September 20, 1982 Disclosure No. 150099/82 Japanese Utility Model Publication 59-73534 ______________________________________